Morphometric analysis of the ventral nerve roots and retroperitoneal vessels with respect to the minimally invasive lateral approach in normal and deformed spines

L4-L5 anatomy classification system for lateral lumbar interbody fusion

Lateral lumbar interbody fusion (LLIF), developed by Dr. Luiz Pimenta in 2006, allows access to the spinal column through the psoas major muscle. The technique has many advantages, such as reduced bone and muscular tissue damage, indirect decompression, larger implants, and lordosis correction capabilities. However, this technique also has drawbacks, with the most notorious being the risk of spinal pathologies due to indirect injury of the lumbar plexus, but with low rates of persistent injuries. Therefore, several groups have proposed classifications to help identify patients at a greater risk of presenting with neurological deficits. The present work proposes a classification system that relies on simple observation of easily identifiable key structures to guide lateral L4-L5 LLIF decision-making. Patients aged > 18 years who underwent preoperative magnetic resonance imaging (MRI) between 2022 and 2023 were included until 50 high-quality images were acquired. And excluded as follow Anatomical changes in the vertebral body or major psoas muscles prevent the identification of key structures or poor-quality MRIs. Each anatomy was classified as type I, type II, or type III according to the consensus among the three observers. Fifty anatomical sites were included in this study. 70% of the L4-L5 anatomy were type I, 18% were type II, and 12% were type III. None of the type 3 L4-L5 anatomies were approached using a lateral technique. The proposed classification is an easy and simple method for evaluating the feasibility of a lateral approach to-L4-L5.

Sequential Depth Stimulation Within the Psoas Offers No Benefit for Localization of the Lumbar Plexus During Lateral Lumbar Fusion Surgery

STUDY DESIGN

Prospective cohort study.

OBJECTIVES

In this study we aim to assess the difference in triggered EMG readings throughout different depths in the psoas muscle during the lateral approach to the lumbar spine and their effect on surgeon decision making.

METHODS

Three surgeons, practicing at different institutions, assessed triggered EMG readings during the trans psoas approach at the level of the disc and 5,10 and 15 millimeters into the psoas muscle with sequential dilators. Measurement of distance into the psoas muscle was done with a specially designed instrument. Results of anterior and posterior directed stimulation as well as the delta value between these were recorded and underwent statistical analysis. Patients who had partial readings were excluded from the study.

RESULTS

A total of 40 levels in 35 patients were included in the study. There was no significant difference found between means of anterior or posterior threshold readings along the different distance groups. A significant difference was found (P = .024) in the mean difference between the distance groups with a decrease in the difference between anterior and posterior threshold values found as the distance from the disc space increased. None of the surgeons reported a decision to abort the fusion of a spinal level.

CONCLUSIONS

In the trans-psoas approach to the lumbar spine, the assessment of the location of the femoral nerve using directional neuromonitoring when advancing in the psoas muscle shows no clear benefit as opposed to stimulating solely when adjacent to the disc space.

Female Sex and Supine Proximal Lumbar Lordosis Are Associated With the Size of the LLIF "Safe Zone" at L4-L5

STUDY DESIGN

Retrospective chart review.

OBJECTIVE

Identify demographic and sagittal alignment parameters that are independently associated with femoral nerve position at the L4-L5 disk space.

SUMMARY OF BACKGROUND DATA

Iatrogenic femoral nerve or lumbar plexus injury during lateral lumbar interbody fusion (LLIF) can result in neurological complications. The LLIF "safe zone" is the anterior half to two third of the disk space. However, femoral nerve position varies and is inconsistently identifiable on magnetic resonance imaging. The safe zone is also narrowest at L4-L5.

METHODS

An analysis of patients with symptomatic lumbar spine pathology and magnetic resonance imaging with a visibly identifiable femoral nerve evaluated at a single large academic spine center from January 1, 2017, to January 8, 2020, was performed. Exclusion criteria were transitional anatomy, severe hip osteoarthritis, coronal deformity with cobb >10 degrees, > grade 1 spondylolisthesis at L4-L5 and anterior migration of the psoas.Standing and supine lumbar lordosis (LL) and its proximal (L1-L4) and distal (L4-S1) components were measured. Femoral nerve position on sagittal imaging was then measured as a percentage of the L4 inferior endplate. A stepwise multivariate linear regression of sagittal alignment and LL parameters was then performed. Data are written as estimate, 95% CI.

RESULTS

Mean patient age was 58.2±14.7 years, 25 (34.2%) were female and 26 (35.6%) had a grade 1 spondylolisthesis. Mean femoral nerve position was 26.6±10.3% from the posterior border of L4. Female sex (-6.6, -11.1 to -2.1) and supine proximal lumbar lordosis (0.4, 0.1-0.7) were independently associated with femoral nerve position.

CONCLUSIONS

Patient sex and proximal LL can serve as early indicators of the size of the femoral nerve safe zone during a transpsoas LLIF approach at L4-L5.

Position of lumbar plexus nerves in the psoas major: Application to transpsoas approaches to the lumbar spine

Far lateral interbody fusion is a minimally invasive operating technique. However, the incidence of postoperative neurological complications is high, and some scholars question its safety. This study describes the neuroanatomical features and spatial orientation within the psoas major. Ten embalmed male cadavers were selected and the left psoas major was dissected. Subsequently, the area between the anterior and the posterior edges of the vertebral body was divided into three equal zones. The nerves' distribution, number, and spatial orientation of the L1/2 to L4/5 intervertebral discs were examined. A caliper was used to measure the diameter of the nerve. The safety zone of the L1/2 intervertebral disc level is located in zone I and II, the relative safe zones of the L2/3 and L4/5 intervertebral discs are located in zone II, and the safety zone of the L3/4 intervertebral disc level is located in the caudal side of zone II. The genitofemoral nerve exits the psoas major in a co-trunk or two-branch pattern, and its exit point was distributed between the L3 and L4 vertebral bodies, mainly at the L3/4 intervertebral disc level. The sympathetic ganglia in the psoas major appeared only in zone I at the L2/3 intervertebral disc level. This is a systematic anatomical study that describes the nerves of the psoas major. Spine surgeons can use this study-which consists of important clinical implications-for preoperative planning, and thus, reduce the risk of nerve injury during surgery.

Anterior Column Realignment: Adult Sagittal Deformity Treatment Through Minimally Invasive Surgery

This article focuses on the treatment of sagittal spinal deformity using a minimally invasive technique, anterior column realignment. Traditional methods to address sagittal spine deformity have been associated with high morbidity, long operative times, and excessive blood loss. This technique uses a minimally invasive lateral retroperitoneal approach to release the anterior longitudinal ligament and apply a hyperlordotic implant for interbody fusion to restore lumbar lordosis and sagittal alignment.

Location of the Femoral Nerve in the Lateral Decubitus Versus Prone Position

STUDY DESIGN

Cadaveric study.

OBJECTIVE

To compare the position of the femoral nerve within the lumbar plexus at the L4-L5 disc space in the lateral decubitus vs prone position.

METHODS

Seven lumbar plexus specimens were dissected and the femoral nerve within the psoas muscle was identified and marked with radiopaque paint. Lateral fluoroscopic images of the cadaveric specimens in the lateral decubitus vs prone position were obtained. The location of the radiopaque femoral nerve at the L4-L5 disc space was normalized as a percentage of the L5 vertebral body (0% indicates posterior location and 100% indicates anterior location at the L4-L5 disc space). The location of the femoral nerve at L4-L5 in the lateral decubitus vs prone position was compared using a paired t test.

RESULTS

In the lateral decubitus position, the femoral nerve was located 28% anteriorly from the posterior edge of the L4-L5 disc space, and in the prone position, the femoral nerve was relatively more posterior, located 18% from the posterior edge of the L4-L5 disc space (P = .037).

CONCLUSIONS

The femoral nerve was on average more posteriorly located at the L4-L5 disc space in the prone position compared to lateral decubitus. This more posterior location allows for a larger safe zone at the L4-L5 disc space, which may decrease the incidence of neurologic complications associated with Lateral lumbar interbody fusion in the prone vs lateral decubitus position; however, further studies are needed to evaluate this possible clinical correlation.

Lateral interbody fusion without intraoperative neuromonitoring in addition to posterior instrumented fusion in geriatric patients: A single center consecutive series of 108 surgeries

Introduction

Lateral lumbar interbody fusion (LLIF) and lateral thoracic interbody fusion (LTIF), supported by intraoperative neuromonitoring (IONM), gained popularity as a mini-invasive alternatives for standard interbody fusion. The objective of this study was to investigate the clinical outcome in a large elderly patient cohort who underwent LTIF/LLIF without IONM.

Methods

This retrospective, single-center study enrolled elderly patients (≥70 years old) operated during the period from 2010 to 2016. Anterior lumbar interbody fusion (ALIF) in the L5/S1 segment was excluded from the analysis.

Results

The study enrolled 108 patients (63 males, 58.3%) with a mean age of 76.5 ​y/o. The mean follow-up was 14.4 ​± ​11.3 months. The mean time of the surgery was 92 ​± ​34.2 ​min. The mean blood loss was 62.2 ​ml. There were no vascular or visceral surgical complications. 39 medical complications were encountered in 24 (22%) patients. Less than 5% of patients presented with a new onset of motor weakness and less than 2% of the patients developed a new sensory deficit at the discharge. 46% of patients were lost in follow-up at 12 months.

Conclusions

IONM is not mandatory for LLIF/LTIF surgery in geriatric patients and has a low frequency of approach-related complications as well as neurological deterioration. Our results are comparable to the available literature. Regardless of the utilization of these mini-invasive, anterior approaches, in patients of advanced aged, the risk for major medical complications is high and is responsible for contributing to prolonged hospitalization.

Postoperative clinical outcomes in patients undergoing MIS-TLIF versus LLIF for adjacent segment disease

PURPOSE

Few studies examine the clinical outcomes in patients undergoing minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) versus lateral lumbar interbody fusion (LLIF) for adjacent segment disease (ASD). We aim to compare the postoperative clinical trajectory through patient-reported outcome measures (PROMs) and minimum clinically important difference (MCID) in patients undergoing MIS-TLIF versus LLIF for ASD.

METHODS

Patients were stratified into two cohorts based on surgical technique for ASD: MIS-TLIF versus LLIF. PROMs of 12-Item Short Form Physical Component Score (SF-12 PCS), visual analog scale (VAS) back, VAS leg, and Oswestry Disability Index (ODI) were collected at preoperative and postoperative 6-week/12-week/6-month/1-year time points. MCID attainment was calculated through comparison to established thresholds. Cohorts were compared through nonparametric inferential statistics.

RESULTS

Fifty-four patients were identified, with 22 patients undergoing MIS-TLIF after propensity score matching. Patients undergoing MIS-TLIF for ASD demonstrated significant postoperative improvement up to 1-year VAS back, up to 1-year VAS leg, and 6-month through 1-year ODI (p ≤ 0.035, all). Patients undergoing LLIF demonstrated significant postoperative improvement in 6-month SF-12 PCS, 6-month through 1-year VAS back, 12-week through 6-month VAS leg, and 6-month to 1-year ODI (p ≤ 0.035, all). No significant differences were calculated between surgical techniques for PROMs or MCID achievement rates.

CONCLUSION

Patients undergoing either MIS-TLIF or LLIF for adjacent segment disease demonstrated significant postoperative improvement in pain and disability outcomes. Additionally, patients undergoing LLIF reported significant improvement in physical function. Both MIS-TLIF and LLIF are effective for the treatment of adjacent segment disease.

Anatomical Analysis of the Gonadal Veins and Spine in Lateral Lumbar Interbody Fusion

BACKGROUND

The current study aimed to investigate the anatomical position of the gonadal veins (GVs) from the viewpoint of spine surgery and the risk factors associated with lateral lumbar interbody fusion (LLIF).

METHODS

This retrospective study included 99 consecutive patients. The GV locations were divided into the ventral (V), dorsal medial (DM), and dorsal lateral (DL) sides based on lumbar disk levels on axial contrast-enhanced computed tomography images. The DM region surrounded by the vertebral body and psoas muscle had the highest risk of GV injury. The GV at each intervertebral disk level was examined in terms of laterality and sex. The patients were divided into group M (which included those with GV in the DM region at any vertebral level) and group O (which included those without GV in the DM region at any vertebral level). Then, the two groups were compared.

RESULTS

In the case of lower lumbar levels and in women, the GVs were commonly observed in the DM region. Group M had a higher incidence of degenerative scoliosis than group O and a significantly larger Cobb angle.

CONCLUSIONS

We should pay close attention to the GV location on the preoperative image when using LLIF, particularly in female patients with degenerative scoliosis.

A retrospective review of single-position prone lateral lumbar interbody fusion cases: early learning curve and perioperative outcomes

PURPOSE

The objective of this study was to discuss our experience performing LLIF in the prone position and report our complications.

METHODS

A retrospective chart review was conducted that included all patients who underwent single- or multi-level single-position pLLIF alone or as part of a concomitant procedure by the same surgeon from May 2019 to November 2022.

RESULTS

A total of 155 patients and 250 levels were included in this study. Surgery was most commonly performed at the L4-L5 level (n = 100, 40%). The most common preoperative diagnosis was spondylolisthesis (n = 74, 47.7%). In the first 30 cases, 3 surgeries were aborted to an MIS TLIF. Complications included 3 unintentional ALL ruptures (n = 3/250, 1.2%), and 1 malpositioned implant impinging on the contralateral foramen requiring revision (n = 1/250, 0.4%), which all occurred within the first 30 cases. Out of 147 patients with more than 6-week follow-ups, there were 3 cases of femoral nerve palsy (n = 3/147, 2.0%). Two cases of femoral nerve palsy improved to preoperative strength by the 6th week postoperatively, while one improved to 4/5 preoperative strength by 1 year. There were no cases of bowel perforation or vascular injury.

CONCLUSION

Our single-surgeon experience demonstrates the initial learning curve when adopting pLLIF. Thereafter, we experienced reproducibility in our technique and large improvements in our operative times, and complication profile. We experienced no technical complications after the 30th case. Further studies will include long-term clinical and radiographic outcomes to understand the complete utility of this approach.

Multimodality Intraoperative Neuromonitoring in Lateral Lumbar Interbody Fusion: A Review of Alerts in 628 Patients

STUDY DESIGN

Retrospective review of private neuromonitoring databases.

OBJECTIVES

To review neuromonitoring alerts in a large series of patients undergoing lateral lumbar interbody fusion (LLIF) and determine whether alerts occurred more frequently when more lumbar levels were accessed or more frequently at particular lumbar levels.

METHODS

Intraoperative neuromonitoring (IONM) databases were reviewed and patients were identified undergoing LLIF between L1 and L5. All cases in which at least one IONM modality was used (motor evoked potentials (MEP), somatosensory evoked potentials (SSEP), evoked electromyography (EMG)) were included in this study. The type of IONM used and incidence of alerts were collected from each IONM report and analyzed. The incidence of alerts for each IONM modality based on number of levels at which at LLIF was performed and the specific level an LLIF was performed were compared.

RESULTS

A total of 628 patients undergoing LLIF across 934 levels were reviewed. EMG was used in 611 (97%) cases, SSEP in 561 (89%), MEP in 144 (23%). The frequency of IONM alerts for EMG, SSEP and MEPs did not significantly increase as the number of LLIF levels accessed increased. No EMG, SSEP, or MEP alerts occurred at L1-L2. EMG alerts occurred in 2-5% of patients at L2-L3, L3-L4, and L4-L5 and did not significantly vary by level (P = .34). SSEP and MEP alerts occurred more frequently at L4-L5 versus L2-L3 and L3-L4 (P < .03).

CONCLUSIONS

IONM may provide the greatest utility at L4-L5, particularly MEPs, and may not be necessary for more cephalad LLIF procedures such as at L1-L2.

Morphometric Analysis of the Ureter with Respect to Lateral Lumbar Interbody Fusion Using Contrast-Enhanced Computed Tomography

OBJECTIVE

To analyze the anatomical location of the ureter in relation to lateral lumbar interbody fusion and evaluate the potential risk of ureteral injury.

METHODS

One hundred eight patients who performed contrast-enhanced computed tomographic scans were enrolled in this study. The location of the ureter from L2-L3 to L4-L5 was evaluated. The distances between the ureter and psoas muscle, intervertebral disc, and retroperitoneal vessels were also recorded bilaterally.

RESULTS

Over 30% of the ureters were close to the working corridor of extreme lumbar interbody fusion at L2-L3. Most of the ureters were close to working corridor of oblique lumbar interbody fusion, especially at L4-L5. The distance from the ureter to the great vessels on the left side was significantly narrowing from L2-L3 to L4-L5 (28.8±9.5 mm, 22.0±8.0 mm, 15.5±8.4 mm), and it was significantly larger than that on the right side (12.3±6.1 mm, 7.4±5.7 mm, 5.4±4.4 mm).

CONCLUSION

Our findings indicate that the location of the ureter varies widely among individuals. To avoid unexpected damage to the ureter, it is imperative to directly visualize it and verify the ureter is not in the surgical pathway during lateral lumbar interbody fusion.

Multilevel tandem spondylolisthesis associated with a reduced "safe zone" for a transpsoas lateral lumbar interbody fusion at L4-5

OBJECTIVE

The aim of this study was to investigate the effect of degenerative spondylolisthesis (DS) on psoas anatomy and the L4-5 safe zone during lateral lumbar interbody fusion (LLIF).

METHODS

In this retrospective, single-institution analysis, patients managed for low-back pain between 2016 and 2021 were identified. Inclusion criteria were adequate lumbar MR images and radiographs. Exclusion criteria were spine trauma, infection, metastases, transitional anatomy, or prior surgery. There were three age and sex propensity-matched cohorts: 1) controls without DS; 2) patients with single-level DS (SLDS); and 3) patients with multilevel, tandem DS (TDS). Axial T2-weighted MRI was used to measure the apical (ventral) and central positions of the psoas relative to the posterior tangent line at the L4-5 disc. Lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and PI-LL mismatch were measured on lumbar radiographs. The primary outcomes were apical and central psoas positions at L4-5, which were calculated using stepwise multivariate linear regression including demographics, spinopelvic parameters, and degree of DS. Secondary outcomes were associations between single- and multilevel DS and spinopelvic parameters, which were calculated using one-way ANOVA with Bonferroni correction for between-group comparisons.

RESULTS

A total of 230 patients (92 without DS, 92 with SLDS, and 46 with TDS) were included. The mean age was 68.0 ± 8.9 years, and 185 patients (80.4%) were female. The mean BMI was 31.0 ± 7.1, and the mean age-adjusted Charlson Comorbidity Index (aCCI) was 4.2 ± 1.8. Age, BMI, sex, and aCCI were similar between the groups. Each increased grade of DS (no DS to SLDS to TDS) was associated with significantly increased PI (p < 0.05 for all relationships). PT, PI-LL mismatch, center psoas, and apical position were all significantly greater in the TDS group than in the no-DS and SLDS groups (p < 0.05). DS severity was independently associated with 2.4-mm (95% CI 1.1-3.8 mm) center and 2.6-mm (95% CI 1.2-3.9 mm) apical psoas anterior displacement per increased grade (increasing from no DS to SLDS to TDS).

CONCLUSIONS

TDS represents more severe sagittal malalignment (PI-LL mismatch), pelvic compensation (PT), and changes in the psoas major muscle compared with no DS, and SLDS and is a risk factor for lumbar plexus injury during L4-5 LLIF due to a smaller safe zone.

Lumbar plexus safe working zones with lateral lumbar interbody fusion: a systematic review and meta-analysis

PURPOSE

Significant risk of injury to the lumbar plexus and its departing motor and sensory nerves exists with lateral lumbar interbody fusion (LLIF). Several cadaveric and imaging studies have investigated the lumbar plexus position with respect to the vertebral body anteroposterior plane. To date, no systematic review and meta-analysis of the lumbar plexus safe working zones for LLIF has been performed.

METHODS

This systematic review was conducted according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Relevant studies reporting on the position of the lumbar plexus with relation to the vertebral body in the anteroposterior plane were identified from a PubMed database query. Quantitative analysis was performed using Welch's t test.

RESULTS

Eighteen studies were included, encompassing 1005 subjects and 2472 intervertebral levels. Eleven studies used supine magnetic resonance imaging (MRI) with in vivo subjects. Seven studies used cadavers, five of which performed dissection in the left lateral decubitus position. A significant correlation (p < 0.001) existed between anterior lumbar plexus displacement and evaluation with in vivo MRI at all levels between L1-L5 compared with cadaveric measurement. Supine position was also associated with significant (p < 0.001) anterior shift of the lumbar plexus at all levels between L1-L5.

CONCLUSIONS

This is the first comprehensive systematic review and meta-analysis of the lumbar neural components and safe working zones for LLIF. Our analysis suggests that the lumbar plexus is significantly displaced ventrally with the supine compared to lateral decubitus position, and that MRI may overestimate ventral encroachment of lumbar plexus.

Rates of Postoperative Complications and Approach-related Neurological Symptoms After L4-L5 Lateral Transpsoas Lumbar Interbody Fusion Compared With Upper Lumbar Levels

STUDY DESIGN

This was a retrospective comparative study.

OBJECTIVE

To compare the likelihood of approach-related complications for patients undergoing single-level lateral lumbar interbody fusion (LLIF) at L4-L5 to those undergoing the procedure at upper lumbar levels.

SUMMARY OF BACKGROUND DATA

LLIF has been associated with a number of advantages when compared with traditional interbody fusion techniques. However, potential risks with the approach include vascular or visceral injury, thigh dysesthesias, and lumbar plexus injury. There are concerns of a higher risk of these complications at the L4-L5 level compared with upper lumbar levels.

MATERIALS AND METHODS

A retrospective cohort review was completed for consecutive patients undergoing single-level LLIF between 2004 and 2019 by a single surgeon. Indication for surgery was symptomatic degenerative lumbar stenosis and/or spondylolisthesis. Patients were divided into 2 cohorts: LLIF at L4-L5 versus a single level between L1 and L4. Baseline characteristics, intraoperative complications, postoperative approach-related neurological symptoms, and patient-reported outcomes were compared and analyzed between the cohorts.

RESULTS

A total of 122 were included in analysis, of which 58 underwent LLIF at L4-L5 and 64 underwent LLIF between L1 and L4. There were no visceral or vascular injuries or lumbar plexus injuries in either cohort. There was no significant difference in the rate of postoperative hip pain, anterior thigh dysesthesias, and/or hip flexor weakness between the cohorts (53.5% L4-L5 vs. 37.5% L1-L4; P=0.102). All patients reported complete resolution of these symptoms by 6-month postoperative follow-up.

DISCUSSION

LLIF surgery at the L4-L5 level is associated with a similar infrequent likelihood of approach-related complications and postoperative hip pain, thigh dysesthesias, and hip flexor weakness when compared with upper lumbar level LLIF. Careful patient selection, meticulous use of real-time neuromonitoring, and an understanding of the anatomic location of the lumbar plexus to the working corridor are critical to success.

The Antepsoas (ATP) Surgical Corridor for Lumbar and Lumbosacral Arthrodesis: A Radiographic, Anatomic, and Surgical Investigation

STUDY DESIGN

Retrospective review of prospectively collected data.

OBJECTIVE

To investigate the size of prepsoas surgical corridors, developed between the iliopsoas and prespinal vessels, at all disk levels between L1 and S1 granted by left and right lateral antepsoas (ATP) approaches. Secondary aims include evaluation of presurgery radiographic prepsoas windows between L1 and S1 with respect to the intraoperative findings.

SUMMARY OF BACKGROUND DATA

The ATP technique is an evolving alternative to the transpsoas and direct anterior exposures for lumbar fusion. However, the vascular morphometric data of the ATP approach remain underexplored, especially at L5-S1.

MATERIALS AND METHODS

Patients indicated for ATP lumbar-lumbosacral fusion between September 2018 and February 2020 were enrolled (n=121). Data were collected prospectively, including the following (in mm): intraoperative manual measurements of the premobilization psoas-vessel (pre-PV) window, the final postmobilization psoas-vessel (post-PV) window, and the preoperative radiographic psoas-to-vessel distance at the respective studied disk levels.

RESULTS

A total of 121 patients (75 female, mean age: 55.3 yr, 81.8% right-sided approach) underwent a total of 279 levels of spinal fusion. Irrespective of the ATP access laterality, we noted ample postmobilization psoas-vessel (post-PV differential) corridors: largest at L4-L5 (36-38 mm) followed by L5-S1 (31-35 mm), L3-L4 (32-33 mm), L2-L3 (28-30 mm), and L1-L2 (20-24 mm). Similarly, the relative increases of the psoas-vessel corridors (post-PV and pre-PV differentials, averaged: 31 mm at L5-S1, 32 mm at L4-L5, 26 mm at L3-L4, 25 mm at L2-L3, and 14 mm at L1-L2) were also significant in both lateral approaches. In right flank approaches, the right vascular structures projected more dorsally compared with left-sided vasculature ( P <0.05).

CONCLUSION

The ATP access offers generous bilateral prepsoas surgical windows to L1-S1 intervertebral disks, allowing for a safe anterior column release, decompression, instrumentation, and fusion.

Anatomical positional changes in the lateral lumbar interbody fusion

INTRODUCTION

ALIFs and LLIFs are now becoming more utilized for adult spinal disease. As technologies advance, so do surgical techniques, with surgeons now modifying traditional supine-ALIF and lateral-LLIF to lateral-ALIF and prone-LLIF approaches to allow for more efficient surgeries. The objective of this study is to characterize the anatomical changes in the surgical corridor that occur with changes in patient positioning.

METHODS

MRIs of ten healthy volunteers were evaluated in five positions: supine, prone with hips flexed, prone with hips extended, lateral with hips flexed, and lateral with hips extended. All lateral scans were in the left lateral decubitus position. The anatomical changes of the psoas muscles, inferior vena cava, aorta, iliac vessels were assessed with relation to fixed landmarks on the disc spaces from L1 to S1.

RESULTS

The most anteriorly elongated ipsilateral to approach psoas when compared to supine was seen in lateral-flexed position (- 5.82 mm, p < 0.001), followed by lateral-extended (- 2.23 mm, p < 0.001), then prone-flexed (- 1.40 mm, p = 0.014), and finally supine and prone-extended (- 0.21 mm, p = 0.643). The most laterally extending or "thickest" psoas was seen in prone-flexed (- 1.40 mm, p = 0.004) and prone-extended (- 1.17 mm, p = 0.002). The psoas was "thinnest" in lateral-extended (2.03 mm, p < 0.001) followed by lateral-flexed (1.11 mm, p = 0.239). The contralateral psoas did not move as anteriorly as the ipsilateral. 3D volumetric analysis showed that the greatest changes in the psoas occur at its proximal and distal poles near T12-L1 and L4-S1. In lateral-flexed compared to prone-extended, the IVC moves medially to the left (p < 0.001). The aorta moves laterally to the left (p = 0.005). The venous structures appeared more full and open in the lateral positions and flattened in the supine and prone positions. The arteries remain in full calibre.

CONCLUSION

The MRI anatomical evaluation shows that the psoas, and therefore lumbar plexus, and vasculature move significantly with changes in positioning. This is important for preoperative planning for proper intraoperative execution from preoperative supine MRI. Understanding that the psoas and vessels move the most anteriorly in the lateral-flexed position and to a least degree in the prone-extended is essential for safe and efficient utilization of techniques such as the traditional LLIF, traditional ALIF, prone-LLIF.

Morphometric analysis of the lumbar vertebrae and intervertebral discs in relation to abdominal aorta: CT-based study

Purpose

Although lumbar discectomy is the most common procedure in spine surgery, reports about anatomical relations between discs and prevertebral vessels are limited. Aim of this research was to investigate morphometric of the lumbar region and the relations between intervertebral discs (IVDs) and abdominal aorta.

Methods

557 abdominal computed tomography scans were assessed. For each spinal column level from Th12/L1 down to L4/L5, we investigated: intervertebral disc’s and vertebra’s height, width, length, and distance from aorta or common iliac artery (CIA). Those arteries were also measured in two dimensions and classified based on location.

Results

54.58% of patients were male. There was a significant difference in arterial-disc distances (ADDs) between genders at the levels: L1/L2 (1.32 ± 1.97 vs. 0.96 ± 1.78 mm; p = 0.0194), L2/L3 (1.97 ± 2.16 vs. 1.15 ± 2.01 mm; p < 0.0001), L3/L4 (2.54 ± 2.78 vs. 1.71 ± 2.61 mm; p = 0.0012), also for both CIAs (left CIA 3.64 ± 3.63 vs. 2.6 ± 3.06 mm; p = 0.0004 and right CIA: 7.96 ± 5.06 vs. 5.8 ± 4.57 mm; p < 0.001)—those ADDs were higher in men at all levels. The length and width of IVD increased alongside with disc level with the maximum at L4/L5.

Conclusion

Bifurcations of the aorta in most cases occurred at the L4 level. Collected data suggest that at the highest lumbar levels, there is a greater possibility to cause injury of the aorta due to its close anatomical relationship with discs. Females have limited, in comparison to males, ADD at L1/L2, L2/L3, and L3/L4 levels what should be taken into consideration during preoperative planning of surgical intervention.

Intraoperative Neuromonitoring During Lateral Lumbar Interbody Fusion

Objective

To review the evidence for the use of electromyography (EMG), motor-evoked potentials (MEPs), and somatosensory-evoked potentials (SSEPs) intraoperative neuromonitoring (IONM) strategies during lateral lumbar interbody fusion (LLIF), as well as discuss the limitations associated with each technique.

Methods

A comprehensive review of the literature and compilation of findings relating to clinical studies investigating the efficacy of EMG, MEP, SSEP, or combined IONM strategies during LLIF.

Results

The evidence for the use of EMG is mixed with some studies demonstrating the efficacy of EMG in preventing postoperative neurologic injuries and other studies demonstrating a high rate of postoperative neurologic deficits with EMG monitoring. Multimodal IONM strategies utilizing MEPs or saphenous SSEPs to monitor the lumbar plexus may be promising strategies based on results from a limited number of studies.

Conclusion

The use of traditional EMG during LLIF remains without consensus. There is a growing body of evidence utilizing multimodal IONM with MEPs or saphenous SSEPs demonstrating a possible decrease in postoperative neurologic injuries after LLIF. Future prospective studies, with clear definitions of neurologic injury, that evaluate different multimodal IONM strategies are needed to better assess the efficacy of IONM during LLIF.

Saphenous Nerve Somatosensory-Evoked Potentials Monitoring During Lateral Interbody Fusion

STUDY DESIGN.

Retrospective cohort study.

OBJECTIVES

To clinically evaluate saphenous nerve somatosensory-evoked potentials (SSEPs) as a reliable and predictable way to detect upper lumbar plexus injury intraoperatively during lateral lumbar trans-psoas interbody fusion (LLIF).

METHODS

Saphenous nerve SSEPs were obtained by stimulation of inferior medial thigh with needle electrodes and recording from transcranial potentials. The primary outcome was measured by testing reproducibility of SSEPs at baseline, changes during the procedure, and relevance to standard modalities. Significant SSEP changes were compared with actual postoperative nerve complications. The sensitivity and specificity of saphenous SSEPs to detect postoperative lumbar plexus nerve injury was calculated.

RESULTS

A total of 62 patients were included in the study. Reliable saphenous SSEPs were recorded on the LLIF approach side in 52/62 patients. Persistent saphenous SSEP reduction of amplitude of >50% in 6 cases was observed during expansion of the tubular retractor or during the procedure. Two of 6 patients postoperatively had femoral nerve sensory deficits, and 5 of 6 patients had mild femoral nerve motor weakness, all of which resolved at an average of 12 weeks postoperatively (range 2-24 weeks). One patient had saphenous SSEP changes but demonstrated intraoperative recovery and had no postoperative clinical deficits. Saphenous SSEPs demonstrated 52% to 100% sensitivity and 90% to 100% specificity for detecting postoperative femoral nerve complications.

CONCLUSION

Saphenous SSEPs can be used to detect electrophysiological changes to prevent femoral nerve injury during LLIF. Intraoperative SSEP recovery after amplitude reduction or loss may be a prognostic factor for final clinical outcome.

Simultaneous Combined Major Arterial and Lumbar Plexus Injury During Primary Extra Lateral Interbody Fusion: Case Report and Review of the Literature

Extra lateral interbody fusion (XLIF) has been established in recent years as an effective approach to address degenerative lumbar disc disease (DLDD). Although neurological and vascular complications during XLIF have been reported, to our knowledge, a combination of simultaneous vascular and neurovascular complication during XLIF has not been reported to date. A 72-year-old female patient was admitted to our orthopaedic department because of back pain associated with severe neuropathic radicular pain to her both lower extremities, incomplete paraplegia and low back fistula with serous secretion for several weeks. She had been wheel-chair bound since nine years before her admission in our department when she had her initial XLIF operation in another institution. Intraoperatively, an aorta lesion occurred, which was emergently addressed, along with lumbar plexus injury. Since then, she had an extensive history of subsequent operations that ended with a T10-S1 posterior lumbar fusion, with no improvement of her neurological condition, complicated by hardware-induced infection. She underwent her last operation in our department; removal of the posterior lumbar construct and extensive debridement of the posterior lumbar spine. We present this rare case and we perform an extensive literature review. Although XLIF has been established in recent years, the report of major vascular injuries, although rare, has questioned its safety profile. Spine surgeons should be aware of catastrophic major neurovascular complications associated with this procedure and be prepared to address them.

Defining a safe working zone for lateral lumbar interbody fusion: a radiographic, cross-sectional study

PURPOSE

To present a radiographic analysis of the anatomy of the lumbar plexus and retroperitoneal blood vessels with respect to psoas morphology and safe working zones (SWZ) for LLIF.

METHODS

A retrospective radiographic analysis of 158 MRI scans was performed. Selected morphometric measurements were performed at L1-L2, L2-L3, L3-L4 and L4-L5 levels: disc anteroposterior distance, psoas anteroposterior distance, lumbar plexus-anterior disc distance, lumbar plexus-anterior psoas distance, vena cava-anterior disc distance and calculation of SWZ in psoas on both left and right sides. The morphometric measurements were analysed for differences with sex and the level.

RESULTS

All the morphometric parameters differed significantly at all levels between males and females. The SWZ was significantly wider on the left side compared to the right-at L2-L3, L3-L4 and L4-L5 levels in females and at L3-L4 and L4-L5 levels in males. The SWZ at L4-L5 was narrowest on both left and right sides-and significantly reduced compared to other levels. 6.9% patients had a SWZ > 20 mm on the left side, and 44.9% patients had SWZ < 20 mm on the right side. With caudal progression of levels, the lumbar plexus and psoas muscle migrated anteriorly and the vena cava/right iliac vein migrated posteriorly.

CONCLUSION

A detailed study of preoperative MRI scans should be carried out in patients planned for LLIF-particularly, at L4-L5 level and in females. A left-sided trans-psoas approach is safer to perform compared to the right side-a right-sided approach should be avoided at L4-L5 considering the narrow SWZ at that level.

A modified procedure of single-level transforaminal lumbar interbody fusion reduces immediate post-operative symptoms: a prospective case-controlled study based on two hundred and four cases

STUDY DESIGN

This is a prospective case-controlled study.

PURPOSE

The purpose of this study is to investigate the effect of a modified transforaminal lumbar interbody fusion (TLIF) on the immediate post-operative symptoms in patients with lumbar disc herniation (LDH) accompanied with stenosis.

METHODS

A total of 204 LDH patients with single-level TLIF were enrolled. According to the sequence of the placement of rods and cage, patients were divided into group R (rod-prior-to-cage) and group C (cage-prior-to-rod). Neurological function was evaluated by the Japanese Orthopedic Association (JOA) score. Radiological assessment includes height of intervertebral space (HIS), foraminal height (FH), foraminal area (FA), and segmental lordosis (SL). Change of original symptoms (pain/numb) and new-onset symptoms (pain/numb) after surgery were also recorded.

RESULTS

Patients in group R had less change of HIS at L3/4, L4/5, and L5/S1 levels compared with pre-operation (all p > 0.05), whereas group C had larger change (all p < 0.05). No statistical difference was found in FH between the two groups before and after surgery at L3/4, L4/5, and L5/S1, respectively (all p > 0.05). In terms of FA, patients in group R had better improvement after surgery than those in group C at L3/4 and L4/5 (both p < 0.05). Patients in both groups acquired good improvement of neurological function. However, there were fewer patients in group R who experienced post-operative leg pain or numb compared with those in group C (p < 0.05).

CONCLUSION

The modified open TLIF can significantly reduce the incidence of immediate post-operative symptoms for patients with single-level lumbar disc herniation via installation of rods prior to insertion of cage and the "neural standard" should serve as the goal of decompression for spine surgeons to restore disc/foraminal height and to minimize nerve distraction.

Anatomic Considerations in the Lateral Transpsoas Interbody Fusion: The Impact of Age, Sex, BMI, and Scoliosis

STUDY DESIGN

This is a retrospective case series.

OBJECTIVE

Define the anatomic variations and the risk factors for such within the operative corridor of the transpsoas lateral interbody fusion.

SUMMARY OF BACKGROUND DATA

The lateral interbody fusion approach has recently been associated with devastating complications such as injury to the lumbosacral plexus, surrounding vasculature, and bowel. A more comprehensive understanding of anatomic structures in relation to this approach using preoperative imaging would help surgeons identify high-risk patients potentially minimizing these complications.

MATERIALS AND METHODS

Age-sex distributed, naive lumbar spine magnetic resonance imagings (n=180) were used to identify the corridor for the lateral lumbar interbody approach using axial images. Bilateral measurements were taken from L1-S1 to determine the locations of critical vascular, intraperitoneal, and muscular structures. In addition, a subcohort of scoliosis patients (n=39) with a Cobb angle >10 degrees were identified and compared.

RESULTS

Right-sided vascular anatomy was significantly more variant than left (9.9% vs. 5.7%; P=0.001). There were 9 instances of "at-risk" vasculature on the right side compared with 0 on the left (P=0.004). Age increased vascular anatomy variance bilaterally, particularly in the more caudal levels (P≤0.001). A "rising-psoas sign" was observed in 26.1% of patients. Bowel was identified within the corridor in 30.5% of patients and correlated positively with body mass index (P<0.001). Scoliosis increased variant anatomy of left-sided vasculature at L2-3/L3-4. Nearly all variant anatomy in this group was found on the convex side of the curvature (94.2%).

CONCLUSIONS

Given the risks and complications associated with this approach, careful planning must be taken with an understanding of vulnerable anatomic structures. Our analysis suggests that approaching the intervertebral space from the patient's left may reduce the risk of encountering critical vascular structures. Similarly, in the setting of scoliosis, an approach toward the concave side may have a more predictable course for surrounding anatomy.

LEVEL OF EVIDENCE

Level 3-study.

Neural decompression in challenging cases: advantages and disadvantages

The peculiarity of extreme lateral interbody fusion (LLIF) is the achievement of indirect neural decompression of the spinal canal while distracting the intervertebral disc space using an interbody cage. In this manuscript we will review the potentials and limitations of this technique when treating degenerative disc disease of the lumbar spine. A literature search of the PubMed-National Library of Medicine was performed. Only articles in English were included. The current available literature demonstrates that LLIF is an effective method to decompress foraminal and central canal stenosis. Based on the current available literature LLIF effects on lateral recess stenosis are less consistent. The aim of this review is to provide with a thorough overview of the latest literature available and provide the audience with targeted-oriented published results that will eventually improve the decision-making process when using the LLIF technique.

Lateral lumbar interbody fusion without intraoperative neuromonitoring: a single-center consecutive series of 157 surgeries

OBJECTIVE

Lateral lumbar interbody fusion (LLIF) is frequently used for anterior column stabilization. Many authors have reported that intraoperative neuromonitoring (IONM) of the lumbar plexus nerves is mandatory for this approach. However, even with IONM, the reported motor and sensory deficits are still considerably high. Thus, the authors' approach was to focus on the indication, trajectory, and technique instead of relying on IONM findings per se. The objective of this study therefore was to analyze the outcome of our large cohort of patients who underwent LLIF without IONM.

METHODS

The authors report on 157 patients included from 2010 to 2016 who underwent LLIF as an additional stabilizing procedure following dorsal instrumentation. LLIF-related complications as well as clinical outcomes were evaluated.

RESULTS

The mean follow-up was 15.9 ± 12.0 months. For 90.0% of patients, cage implantation by LLIF was the first retroperitoneal surgery. There were no cases of surgery-related hematoma, vascular injury, CSF leak, or any other visceral injury. Between 1 and 4 cages were implanted per surgery, most commonly at L2-3 and L3-4. The mean length of surgery was 92.7 ± 35 minutes, and blood loss was 63.8 ± 57 ml. At discharge, 3.8% of patients presented with a new onset of motor weakness, a new sensory deficit, or the deterioration of leg pain due to LLIF surgery. Three months after surgery, 3.5% of the followed patients still reported surgery-related motor weakness, 3.6% leg pain, and 9.6% a persistent sensory deficit due to LLIF surgery.

CONCLUSIONS

The results of this series demonstrate that the complication rates for LLIF without IONM are comparable, if not superior, to those in previously reported series using IONM. Hence, the authors conclude that IONM is not mandatory for LLIF procedures if the surgical approach is tailored to the respective level and if the visualization of nerves is performed.

Lumbar Interbody Fusions for Degenerative Spondylolisthesis: Review of Techniques, Indications, and Outcomes

STUDY DESIGN

Broad narrative review.

OBJECTIVES

To review and summarize the current literature on the outcomes, techniques, and indications of lumbar interbody fusion in degenerative spondylolisthesis.

METHODS

A thorough review of peer-reviewed literature was performed on the outcomes, techniques, and indications of lumbar interbody fusions in degenerative spondylolisthesis.

RESULTS

A number of studies have found similar results between interbody fusions and posterolateral fusion in the setting of degenerative spondylolisthesis. There is some evidence that suggests that interbody fusion may be a useful adjunct in the setting of unstable degenerative spondylolisthesis. The number of options for interbody fusions has quickly expanded. Initially, interbody fusions were accomplished via an anterior approach. Posterior and transforaminal interbody fusions are 2 options that accomplish an interbody fusion without the morbidity of an anterior approach. Over the past decade, minimally invasive options including extreme lateral, oblique, and minimally invasive transforaminal interbody fusions have gained popularity.

CONCLUSIONS

Lumbar interbody fusion can be a useful tool in the setting of unstable degenerative spondylolisthesis. A number of technique options, both open and minimally invasive, are available to accomplish an interbody fusion. The literature to this date does not support a clear benefit of one technique over others in the setting of degenerative spondylolisthesis.

Vertebral Body Rotation in Patients with Lumbar Degenerative Scoliosis: Surgical Implication for Oblique Lumbar Interbody Fusion

BACKGROUND

To investigate changes of oblique corridor in patients with lumbar degenerative scoliosis and determine proper working angle with respect to the direction of vertebral axial rotation during the oblique lumbar interbody fusion procedure.

METHODS

The distance of oblique corridor and the rotational angle of the left or right apex group were measured on axial T2 magnetic resonance images and then compared with those of the propensity score-matched control group.

RESULTS

Fifty-five patients of the left apex group and 57 patients of the right apex group were compared with the equal number of patients of the propensity score-matched control group. The distance of oblique corridor in the left apex group was shorter than that in the control group at the levels of L1-2 and L2-3. In contrast, the distance of oblique corridor in the right apex group was longer than that of the control group at the level of L2-3. Patients of the left apex group showed the vertebral body rotating to the left side from L1-2 to L5-S1, whereas in the right apex group, the vertebral body rotated to the right side at the levels of L1-2, L2-3, and L3-4.

CONCLUSIONS

In the left apex group, the oblique corridor was decreased from psoas overlap, and coupled axial rotation to the left side might increase the risk of contralateral nerve root injury during orthogonally working. Thus, surgeons should pay attention to the state of coupled vertebral axial rotation of lumbar degenerative scoliosis for the oblique lumbar interbody fusion procedure.

COMPARATIVE STUDY OF LUMBAR PLEXUS PATH ON THE LEFT AND RIGHT SIDES THROUGH THE PSOAS MUSCLE

ABSTRACT Objective: Spine surgery with a minimally invasive lateral approach and validate possible anatomical differences between the right and left sides. Methods: Four measurements (cm) were taken on 38 cadavers: the distance between the lumbar plexus and the transverse process (L4-L5) and the distance between the lumbar plexus and the midline of the lumbar spine, both on the right and left sides. Results: The mean distance between the lumbar plexus and the transverse process of L4-L5 was 1.03 cm and the distance to the midline was 3.99 cm for the right side. The averages of the left side were 1.13 cm and 3.38 cm, respectively. There is statistical difference between the sides (p<0.05) using the non-parametric Wilcoxon test. Conclusions: The authors suggest that the transverse process might be used as an anatomical landmark to define the surgical approach through the psoas muscle. Level of Evidence IV; Cadaveric study.

Relation of lumbar sympathetic chain to the open corridor of retroperitoneal oblique approach to lumbar spine: an MRI study

BACKGROUND

Retroperitoneal oblique approach to lumbar spine used surgical corridor between psoas muscle and aorta for exposure to anterior part of lumbar spine. Lumbar sympathetic chain (LSC) runs in the corridor to make it a structure at risk of injury.

RESEARCH QUESTION

Does LSC relationship with surgical corridor for minimally invasive retroperitoneal anterolateral oblique approach change in different intervertebral disc level?

METHODS

Left LSC was identified in axial magnetic resonance imaging images at L2-3, L3-4 and L4-5 intervertebral disc levels of 144 patients. Distances between LSC and left psoas muscle and aorta were recorded.

RESULTS

Mean age of the patients was 62.3 years. LSC was identifiable in 90.9% of levels. Distance between LSC and psoas muscle at L2-3, L3-4 and L4-5 was 4.0 mm, 4.7 mm and 5.2 mm. Statistical difference was found between L2-3 and L4-5 level (p = 0.006). Distance between LSC and aorta at each level was 12.4 mm, 12.3 mm and 10.6 mm without statistical difference. In non-scoliosis group distance between LSC and psoas muscle at each level was 3.1 mm, 3.3 mm and 4.0 mm. Statistical difference was found between L2-3 and L4-5 level (p = 0.012) and between L3-4 and L4-5 level (p = 0.041). Distance between LSC and aorta at each level was 11.9 mm, 11.4 mm and 10.2 mm. Statistical difference was found between L2-3 and L4-5 disc level (p = 0.039).

CONCLUSION

LSC moves away from psoas muscle and becomes closer to aorta in L4-5 disc level. These slides can be retrieved under Electronic Supplementary Material.

Management of aortic injury during minimally invasive lateral lumbar interbody fusion

PURPOSE

Minimally invasive lateral approaches to the lumbar spine allow for interbody fusion with good visualization of the disk space, minimal blood loss, and decreased length of stay. Major neurologic, vascular, and visceral complications are rare with this approach; however, the steps in management for severe vascular injuries are not well defined. We present a case report of aortic injury during lateral interbody fusion and discuss the use of endovascular repair.

METHODS

This study is a case report of an intraoperative aortic injury.

RESULTS

A 59-year-old male with ankylosing spondylitis suffered an acute L1 Chance fracture after mechanical fall. He was taken to the operating room for a T10-L4 posterior instrumented fusion followed by a minimally invasive L1-L2 lateral interbody fusion for anterior column support. During the discectomy, brisk arterial bleeding was encountered due to an aortic injury. The vascular surgery team expanded the incision in an attempt to control the bleeding but with limited success. The patient underwent intraoperative angiogram with placement of stent grafts at the level of the injury followed by completion of the interbody fusion. Despite the potentially catastrophic nature of this injury, the patient made a good recovery and was discharged home in stable condition with no new neurologic deficits.

CONCLUSIONS

This case highlights the importance of immediate recognition and imaging of any potential vascular injury during minimally invasive lateral interbody fusion. Given the poor outcomes associated with attempted open repair, endovascular techniques provide a valuable tool for the treatment of these complex injuries with significantly less morbidity.

Relationship between Displacement of the Psoas Major Muscle and Spinal Alignment in Patients with Adult Spinal Deformity

Study Design

Cross sectional study.

Purpose

To clarify the difference in position of the psoas muscle between adult spinal deformity (ASD) and lumbar spinal stenosis (LSS).

Overview of Literature

Although it is known that the psoas major muscle deviates in ASD patients, no report is available regarding the difference in comparison with LSS patients.

Methods

This study investigates 39 patients. For evaluating spinal alignment, pelvic tilt (PT), pelvic incidence (PI), sacral slope, lumbar lordosis (LL), PI–LL, Cobb angle, and the convex side, the lumbar curves were measured. For measuring the position of the psoas major at the L4/5 disk level, magnetic resonance imaging was used. The displacements of psoas major muscle were measured separately in the anterior–posterior and lateral directions. We examined the relationship between the radiographic parameters and anterior displacement (AD) and lateral displacement (LD) of the psoas major muscle.

Results

AD was demonstrated in 15 cases with ASD and nine cases with LSS (p>0.05). LD was observed in 13 cases with ASD and no cases with LSS (p<0.01). The Cobb angle was significantly greater in cases with AD than in those without AD (p=0.04). PT, LL, PI–LL, and Cobb angle were significantly greater in cases with LD (p<0.05). All cases with LD had AD, but no case without AD had LD (p<0.001). The side of greater displacement at L4/5 and the convex side of the lumbar curve were consistent in all cases.

Conclusions

Despite AD being observed in LSS as well, LD was observed only in the ASD group. Radiographic parameters were worse when LD was seen, rather than AD.

Minimally invasive spine surgery for degenerative spine disease and deformity correction: a literature review

During the last two decades, minimally invasive techniques and instruments in spine surgery have undergone serious development in all fields. Specific advantages of these minimally invasive methods have put them forward in spine surgery in recent times. Preservation of important anatomical structures of the spine is a major factor for the evolution of these procedures. The lower prevalence of complications and faster rehabilitation of patients are some of the advantages of minimally invasive spine surgery (MISS). Due to the increasing use of minimally invasive methods in the clinical practice worldwide, there is a strong need for clarification of basic principles, tips and tricks, complications, and clinical outcomes. This review is an effort to provide a better understanding of some of these procedures.

Psoas Morphology Differs between Supine and Sitting Magnetic Resonance Imaging Lumbar Spine: Implications for Lateral Lumbar Interbody Fusion

Study Design

Retrospective radiological review.

Purpose

To quantify the effect of sitting vs supine lumbar spine magnetic resonance imaging (MRI) and change in anterior displacement of the psoas muscle from L1–L2 to L4–L5 discs.

Overview of Literature

Controversy exists in determining patient suitability for lateral lumbar interbody fusion (LLIF) based on psoas morphology. The effect of posture on psoas morphology has not previously been studied; however, lumbar MRI may be performed in sitting or supine positions.

Methods

A retrospective review of a single-spine practice over 6 months was performed, identifying patients aged between 18–90 years with degenerative spinal pathologies and lumbar MRIs were evaluated. Previous lumbar fusion, scoliosis, neuromuscular disease, skeletal immaturity, or intrinsic abnormalities of the psoas muscle were excluded. The anteroposterior (AP) dimension of the psoas muscle and intervertebral disc were measured at each intervertebral disc from L1–L2 to L4–L5, and the AP psoas:disc ratio calculated. The morphology was compared between patients undergoing sitting and/or supine MRI.

Results

Two hundred and nine patients were identified with supine-, and 60 patients with sitting-MRIs, of which 13 patients had undergone both sitting and supine MRIs (BOTH group). A propensity score match (PSM) was performed for patients undergoing either supine or sitting MRI to match for age, BMI, and gender to produce two groups of 43 patients. In the BOTH and PSM group, sitting MRI displayed significantly higher AP psoas:disc ratio compared with supine MRI at all intervertebral levels except L1–L2. The largest difference observed was a mean 32%–37% increase in sitting AP psoas:disc ratio at the L4–L5 disc in sitting compared to supine in the BOTH group (range, 0%–137%).

Conclusions

The psoas muscle and the lumbar plexus become anteriorly displaced in sitting MRIs, with a greater effect noted at caudal intervertebral discs. This may have implications in selecting suitability for LLIF, and intra-operative patient positioning.

Complications Associated With Lateral Interbody Fusion: Nationwide Survey of 2998 Cases During the First 2 Years of Its Use in Japan

STUDY DESIGN

Retrospective nationwide questionnaire-based survey of complications.

OBJECTIVE

To elucidate the incidence of complications and risk factors associated with lateral interbody fusion (LIF).

SUMMARY OF BACKGROUND DATA

After its introduction to Japan in February 2013, the numbers of LIF cases have increased substantially because of the advantages of this minimally invasive procedure. However, LIF has the potential risk of several complications unique to the procedure. Although there are many reports of complications, no nationwide survey has been conducted.

METHODS

Questionnaires were sent to all Japanese Society for Spine Surgery and Related Research (JSSR) members. Questionnaires requested information about surgical procedures (XLIF or OLIF), patient characteristics, preoperative diagnosis, complications, salvage procedures, final outcomes, and the surgeon's experience of LIF. The data from replies received between March 2013 and April 2015 were recorded on a web site and the details of complications were analyzed by a JSSR research team.

RESULTS

Seventy-one institutions (12.3%) answered "yes" to LIF experience and 2998 cases (1995 XLIF and 1003 OLIF) were enrolled in this study. The response rate was 86.1%. A total of 540 complications were reported, of which 474 (84.8%) could be further analyzed. The overall complication rate was 18.0%. The most frequent complications were sensory nerve injury (5.1%) and psoas weakness (4.3%) and the majority resolved spontaneously. The rates of major vascular injury, bowel injury, and surgical site infection were 0.03%, 0.03%, and 0.7%, respectively. The overall reoperation rate was 2.2%. Higher rates of sensory nerve injury and psoas weakness were reported for XLIF and higher rates of peritoneal laceration and ureteral injury were reported for OLIF.

CONCLUSION

A nationwide survey of complications associated with LIF was conducted. Although the majority of complications were minor, a relatively high rate of complications was reported. Approach-related specific features of the two procedures were identified.

LEVEL OF EVIDENCE

4.

Lateral lumbar interbody fusion: a systematic review of complication rates

BACKGROUND CONTEXT

Lateral lumbar interbody fusion (LLIF) is a frequently used technique for the treatment of lumbar pathology. Despite its overall success, LLIF has been associated with a unique set of complications. However, there has been inconsistent evidence regarding the complication rate of this approach.

PURPOSE

To perform a systematic review analyzing the rates of medical and surgical complications associated with LLIF.

STUDY DESIGN

Systematic review.

PATIENT SAMPLE

6,819 patients who underwent LLIF reported in clinical studies through June 2016.

OUTCOME MEASURES

Frequency of complications within cardiac, vascular, pulmonary, urologic, gastrointestinal, transient neurologic, persistent neurologic, and spine (MSK) categories.

METHODS

This systematic review was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Relevant studies that identified rates of any complication following LLIF procedures were obtained from PubMed, MEDLINE, and EMBASE databases. Articles were excluded if they did not report complications, presented mixed complication data from other procedures, or were characterized as single case reports, reviews, or case series containing less than 10 patients. The primary outcome was frequency of complications within cardiac, vascular, pulmonary, urologic, gastrointestinal, transient neurologic, persistent neurologic, and MSK categories. All rates of complications were based on the sample sizes of studies that mentioned the respective complications. The authors report no conflicts of interest directly or indirectly related to this work, and have not received any funds in support of this work.

RESULTS

A total of 2,232 articles were identified. Following screening of title, abstract, and full-text availability, 63 articles were included in the review. A total of 6,819 patients had 11,325 levels fused. The rate of complications for the categories included were as follows: wound (1.38%; 95% confidence interval [CI]=1.00%-1.85%), cardiac (1.86%; CI=1.33%-2.52%), vascular (0.81%; CI=0.44%-1.36%), pulmonary (1.47; CI=0.95%-2.16%), gastrointestinal (1.38%; CI=1.00%-1.87%), urologic (0.93%; CI=0.55%-1.47%), transient neurologic (36.07%; CI=34.74%-37.41%), persistent neurologic (3.98%; CI=3.42%-4.60%), and MSK or spine (9.22%; CI=8.28%-10.23%).

CONCLUSIONS

The current study is the first to comprehensively analyze the complication profile for LLIFs. The most significant reported complications were transient neurologic in nature. However, persistent neurologic complications occurred at a much lower rate, bringing into question the significance of transient symptoms beyond the immediate postoperative period. Through this analysis of complication profiles, surgeons can better understand the risks to and expectations for patients following LLIF procedures.

Variation in Psoas Muscle Location Relative to the Safe Working Zone for L4/5 Lateral Transpsoas Interbody Fusion: A Morphometric Analysis

BACKGROUND

The safe working zone for lateral access to the L4/5 disc space has been said to lie in the anteroposterior (AP) midpoint of the disc space due to the location of the femoral nerve at that level. However, the AP location of the psoas muscle (and thus the lumbosacral plexus within) at L4/5 is variable. A psoas muscle lying excessively anteriorly at the L4/5 disc space may preclude safe access to the L4/5 disc space from a lateral transpsoas approach.

METHODS

Lumbar spine magnetic resonance imaging (MRI) for 300 consecutive patients at the authors' institution were reviewed retrospectively. The AP distance between the ventral aspect of the thecal sac and the dorsal aspect of the psoas muscle at L4/5 was measured, as was the AP diameter of the L4/5 disc space.

RESULTS

The dorsal aspect of the psoas muscle at L4/5 was most commonly found dorsal to the ventral aspect of the thecal sac (zone P, N = 145; 48.3%), whereas it was found at the junction of zones IV/P in 37 patients (12.3%), in zone IV in 85 patients (28.3%), in zone III in 29 patients (9.7%), and in zone II in 4 patients (1.3%).

CONCLUSIONS

The location of the psoas muscle in relation to the L4/5 disc space is somewhat variable. In 11% of patients, the dorsal-most aspect of the psoas muscle was located within zones II or III, likely precluding safe access to the L4/5 disc space from a lateral transpsoas approach.

Morphometric Analysis of the Retroperitoneal Vessels With Respect to Lateral Access Surgery in Adult Scoliosis

STUDY DESIGN

Cross-sectional study reviewing 62 magnetic resonance imaging or computed tomography scans from consecutive adult patients with scoliotic spinal deformity in the thoracolumbar spine.

OBJECTIVE

To investigate the variation in anatomic position of retroperitoneal vessels in relationship to curve direction, location, magnitude, and axial rotation of curves in adult scoliosis.

SUMMARY OF BACKGROUND DATA

The minimally invasive lateral approach to the thoracolumbar spine avoids manipulation of abdominal and retroperitoneal structures and decreases risk of injury to paraspinal musculature. In adult patients with scoliosis, the varying anatomic relationship between retroperitoneal vessels and intervertebral disk spaces can increase the risk of vascular injury.

MATERIALS AND METHODS

Axial images were used to measure the anterior-posterior diameter of the inferior vertebral endplate with respect to the disk space perpendicular to the widest length of the disk. The overlap of the retroperitoneal vessels with the endplate were measured at the cephalad end vertebra, apex, and caudad end vertebra of each curve. Overlap and accessible disk space for individual disk spaces were also measured.

RESULTS

There was a significant difference in percentage overlap of the apex and cephalad vertebral endplate and inferior vena cava in right versus left-sided curves (P=0.002). Overlap between the inferior vertebral endplate and inferior vena cava at the cephalad, apex, and caudad end of the curve was significantly different between thoracolumbar and lumbar curves (P<0.05). Axial rotation significantly affected vessel overlap at multiple curve locations. There was a statistically significant difference in accessible disk space when approaching the curve from the concavity versus convexity.

CONCLUSIONS

Overlap between retroperitoneal vessels and inferior vertebral endplates at the disk level in scoliotic spines varies significantly with direction of the curvature, level of the deformity, and degree of axial rotation. There is decreased accessible disk space and increased vessel overlap on the concavity of the curve. Surgeons, as usual, will take an individualized case by case approach to avoid approach-related vascular complications, but the general relationships reported in this study can guide side of approach.

Relationship of the lumbar plexus branches to the lumbar spine: anatomical study with application to lateral approaches

BACKGROUND CONTEXT

Injuries to the lumbar plexus during lateral approaches to the spine are not uncommon and may result in permanent deficits. However, the literature contains few studies that provide landmarks for avoiding the branches of the lumbar plexus.

PURPOSE

The present anatomical study was performed to elucidate the course of these nerves in relation to lateral approaches to the lumbar spine.

STUDY DESIGN

This is a quantitative anatomical cadaveric study.

METHODS

The lumbar plexus and its branches were dissected on 12 cadaveric sides. Metal wires were laid on the nerves along their paths on the posterior abdominal wall. Fluoroscopy was performed in the anteroposterior and lateral positions. The relationships between regional bony landmarks and the branches of the lumbar plexus were observed.

RESULTS

When viewed laterally, the greatest concentration of nerves occurred from the posteroinferior aspect of L4, inferior along the posterior one-third of the body of L5, then at the level of the sacral promontory. On the basis of our study, approaches to the anterior two-thirds of the L4 vertebra and anterior third of L5 will result in the lowest chance of lumbar plexus nerve injury. In addition, lateral muscle dissection through the psoas major should be in a superior to inferior direction in order to minimize nerve injury. Laterally, the widest corridor between branches in the abdominal wall was between the subcostal and iliohypogastric nerves.

CONCLUSIONS

The findings of our cadaveric study provide surgeons who approach the lateral lumbar spine with data that could decrease injuries to the branches of the lumbar plexus, thus lessening patient morbidity.